In the last decade, progressive developments in computer hardware, software, manufacturing technologies, and dental materials consistently enhanced the use of digital technologies in dentistry. Traditional prosthodontic techniques have relied on manual fabrication processes, which often resulted in challenges such as suboptimal prosthesis fit, compromised occlusal stability, and limited customization options. However, the advent of 3D printing technology has revolutionized the field, offering new possibilities for patient-specific prosthodontic rehabilitation.

An accurate maxillomandibular relationship between the maxillary and mandibular casts is fundamental to prosthodontic practice. In the integration of intraoral scanners (IOSs) for different dental interventions, the accuracy of the digitizing methods recording the maxillomandibular relationship is similarly essential. The maxillomandibular relationship accuracy recorded by using IOSs has been analyzed in various in vitro and clinical studies.

Intraoral digital scans are recorded in an unload condition, with the mouth open, while acquiring the maxillary and the mandibular intraoral scans. This condition changes when capturing the virtual occlusal records at maximum intercuspation position (MIP). Occlusal collisions are caused by the tooth location discrepancy resulting from the periodontal ligament plasticity between the recording of the intraoral digital scans and the virtual occlusal records, as well as from the intraoral scanning distortion and alignment procedures.

Artificial intelligence driven program software and occlusal collisions or mesh interpenetrations tools have been proposed to improve the maxillomandibular relationship of the scanned models. The software programs of the IOSs can automatically eliminate the occlusal collisions present in virtual articulated casts. Similarly, dental computer-aided design (CAD) programs can automatically detect and eliminate occlusal collisions among the articulated intraoral digital scans imported. However, the effect of the occlusal collision corrections performed by using IOSs or CAD programs on the occlusal adjustment of the restorations is unknown.

Objectives The goal of this clinical investigation is to assess the impact of occlusal collision corrections performed by the software program of 2 intraoral scanners (TRIOS 4; 3Shape A/S, i700; Medit) and two dental CAD programs (DentalCAD, Rijeka; exocad & Dental System ;3Shape), for maxillomandibular relationship acquired at maximum intercuspation position, on the intraoral occlusal adjustment of 3D-printed restorations. The null hypothesis was that no difference would be found for the intraoral occlusal adjustment of the assessed 3D-printed restorations, designed by the different collision correction methods, independently of the IOS and the dental CAD software.

Materials and methods In total 30 patients are going to be enrolled in the present study. Initially, two intraoral scanners will be used to record the experimental digital scans: TRIOS 4 (TRIOS 4, wireless, v. 22.2.3; 3Shape A/S) and i700 (i700, Medit). Two groups will be established depending on the correction of the occlusal collisions performed by using the IOS software program: not corrected and corrected group. Moreover, 3 subgroups will be established based on the following correction procedures performed in a dental CAD program (DentalCAD, Rijeka; exocad GmbH): no changes, cast trimming (trimming subgroup), opening of the vertical dimension (opening subgroup).

For each record a model-free complete digital workflow will be employed to print a crown using a 3D printer (Pro 2, Sprintray) with a compatible resin (KeyDenture Try-in, KeystoneIndustries). Each restoration is going to be tried and fit intraorally. The sequence of try-in will be randomized. Initially, after adjusting for distal and mesial approximal contact areas, the internal fit will be checked and adjusted to eliminate any interferences in order to ensure the optimal fitting of the restorations. After ensuring optimal fitting, the investigator will take an intraoral quadrant scan including the crown.

The occlusal adjustment strategy will be as follows: Under normal occlusal forces, 8 μm articulating film (AccuFilm, FastCheck, Parkell) will be used consecutively, followed by occlusal contact check using 8 μm articulation foil (Shimstock-foil, Bausch, Cologne, Germany) under strong occlusal forces. Then the occlusal adjustments will be made with fine diamond burs and will polished. After that, the same investigator will take in intraoral digital quadrant scan to record the post-adjustment volume of the each crown.

For the qualitative analysis, color-coded maps of the superimposed pre- and post-adjustment .STL files will be used, utilizing metrology software (Geomagic, 3DSystems). The primary outcome measure will be the volumetric measurement (mm3) of occlusal adjustment amount of the tested 3D printed restorations. The color codes will be standardized in every evaluation, and the occlusal views of color-coded maps will be evaluated by two investigators independently. Less than 0.3 mm differences which were presented in green and yellow, are going to be considered clinically as irrelevant. Meanwhile, turquoise (0.3-04mm), dark blue (0.4-0.5 mm), and red (>0.5 mm) will be taken into consideration for the evaluation. The investigators will rate the adjustment amount 0-4 scores based on the adjustment surface, and the geometrical characteristics of the adjustment. Grade 4 adjustments will be considered to require renewal of the restoration due to a change in the anatomical contour of the reconstructions, whereas Grade 0 will be considered as perfect.

Inclusion criteria Age > 18 years old Absence of painful temporomandibular disorder Presence of natural opposing teeth Presence of a stable maximum intercuspation relationship Exclusion criteria Pain in orofacial region Visible periapical lesion < Class II mobility

Statistical Analysis The descriptive statistics will be given as mean (standard deviation) and median [first and third quartiles] for continuous variables, while frequency and percentages will be given for categorical variables. The 2 × 2 cross-table variance analyses and Greenhouse Geisser corrections will be tested for the carry-over effect. The two dependent and independent variables will be compared via the Wilcoxon and Mann-Whitney U tests, respectively. For the 2 × 2 crossover design, repeated measure ANOVA will be implemented. The Wilcoxon test analyzed the operator and patient preferences outcomes. Statistical analysis will be performed using a statistical software program (SPSS Statistics, v23.0; IBM Corp, New York, USA). The significance level will set at p<0.05.

Inclusion Criteria:

Age > 18 years old Absence of painful temporomandibular disorder Presence of opposing teeth Presence of a stable maximum intercuspation relationship

Exclusion Criteria:

- Pain in orofacial region Visible periapical lesion < Class II mobility

Only IPD used in the results publication